Chapter 6. Functional Programming

Functional programming is a different approach to development than the heavily object oriented approach that we have focused on so far. Object oriented programming is a fantastic tool for solving a great number of problems but it has some issues. Parallel programming within an object oriented context is difficult as the state can be changed by various different threads with unknown side effects. Functional programming does not permit state or mutable variables. Functions act as primary building blocks in functional programming. Places where you might have used a variable in the past will now use a function.

Even in a single threaded program, functions can have side-effects that change global state. This means that, when calling an unknown function, it can alter the whole flow of the program. This makes debugging a program quite difficult.

JavaScript is not a functional programming language but we can still apply some functional principles to our...